High-frequency amplifier



Jan. 20, 1948.

c. E DOLBERG HIEGH-FREQUENCY AMPLIFIER Filed May 50, 1944 2 Sheets-Sheet l /Fece/yer 5%455/3 y/KQHW Jan. 20, 1948. I c, DQLBERG 2,434,792

HIGH-FREQUENCY AMPLIFIER Filed May 30, 1944 2 Sheets-Sheet 2 fiaiifg" 9 @24 j WhW Patented Jan. 20, 1948 UNITED STATES PATENT OFFICE HIGH-FREQUEN CY AMPLIFIER Charles E. Dolberg, Philadelphia, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application May 30, 1944, Serial No. 538,064

11 Claims. 1

The invention relates to high frequency amplifiers, and more particularly to the tuned coupling circuits between amplifier stages, the principal object of the invention being to provide a novel device for eliminating the usual external tuned circuit with its associated lead inductances and capacitances. The invention is adapted for use, for example, in 60 megacycle I. F. amplifier circuits and it will be described with reference to such use, but it Will be understood that the invention is not limited thereto and is capable of use in any instance where cascaded high frequency amplifiers are desired.

The invention is also particularly adapted largely for eliminating the lead inductance in the Wiring associated with the conventional external tuned circuit and for eliminating the stray ca pacities normally associated with such leads and with the conventional terminal pins and socket contacts. Accordingly, by means of the present invention, the use of higher L/C ratios is permltted, and consequently the gain per stage is correspondingly increased.

It is an object of the present invention to provide a high gain amplifier stage which is characterized by unusual stability of operation at high frequencies.

Still another object of the invention is to provide a simple and economical tuned circuit arrangement that will allow compact mounting of several I. F. amplifier stages,

These and other objects of the present invention will become apparent from the following detailed description when considered in connection with the accompanying drawings, in which:

Fig. 1 is a schematic diagram of a conventional amplifier circuit to which the present invention may be applied;

Fig. 2 is a perspective view, partly schematic in character, of an improved high frequency amplifier tube constructed in accordance with the principles of the present invention; and

Fig. 3 is an elevational view of a plurality of the devices of Fig. 2 connected in cascade.

The two-stage high frequency amplifier circuit of Fig. 1 comprises a pair of vacuum tubes V1 and V2 coupled, in conventional manner, by means of a coupling condenser 2 and a resonant circuit comprising the inductance coil 3 and the associated capacitances 5, 6, and l. In conventional systems the coil 3 is frequently tuned by means of a slug or a threaded brass screw (not shown) adjustably introduced in the coil or winding 3. An alternative and improved method of 2 tuning this resonant circuit will be described hereinafter.

As above indicated, a principal purpose of the present invention is to obviate certain objectional characteristics of high frequency amplifier stages caused by external tuned circuits. As has been stated, it has been customary to tune the said external circuits by means of a tuning slug associated with the coil 3 of Fig. 1. Such an arrangement varies the inductance in order to resonate the coil with the tuning capacities which include the output capacity 5 of V1, the input capacity 6 of V2, and the associated socket and lead capacities (distributed capacities) represented by condenser l. The distributed capacity I usually is greater than the sum of the output and input capacities 5 and 6, even under the best of operating conditions. If the tuned circuit could be arranged so that the coil and lead inductances were lumped, and the distributed capacities eliminated, a more desirable form of the tuned circuit and coupling arrangement would be obtained. In addition, a higher gain would be possible since the L/C ratio may be substantially increased. The present invention provides a simple and economic arrangement by which the stray capacity is substantially eliminated and by which th inductance is lumped, whereby the objectionable characteristics are practically eliminated.

Referring now to Fig. 2, which illustrates a preferred form of the present invention, it will be seen that the tube shown is conventional with respect to most of its electrodes, specifically the heater (not shown), cathode 8, control grid 9, screen grid l0, and suppressor grid 1 I, The cylindrical structure l2, which constitutes the plate or anode of the tube, has its lower portion open and its top closed except for an aperture designated by the reference character l3. As shown, the cylindrical anode fits directly over the structure comprising the elements hereinbefore mentioned. The electrode assembly may be supported in the usual manner (not shown).

A corrugated metallic diaphragm I 4 is positioned above the anode l2 and cooperates with the top surface thereof to provide a predetermined capacitance which may be varied by moving the central part of the diaphragm, the outer edge of which is secured to the grounded metal shell of the tube. The aperture l3 establishes the desired area of the top of the anode. The diaphragm l4 also serves as one wall of the evacuated chamber.

A screw l5, threadedly engaging the top of the tube, serves to adjust the diaphragm It. To this described above.

end, the lower end of the screw is swiveled in a bearing l6 attached to the diaphragm.

Inserted between the lower portion of the control grid 9 and its pin 24 in the tube base there is suitably mounted on the base of the tube a cylindrical glass form H, on which a coil [8 is wound. For simplicity, the contact prongs or pins for the other electrodes are omitted. In this instance, the pin 24serves to connect the lower end of coil I8 to ground. The coil l8 has an inductance in the neighborhood of the lead and winding inductance of the external coupling circuit shown in Fig. 1, and will resonate Witha capacity equal to the output and input capacities and 6 respectively of Fig. 1 atthe desired frequency. By means of a suitable coupling condenser l9 (preferably of the ceramic type), one lead of which is connected to the'junction of grid 9 and coil l8, coupling between stage may be obtained by passing the other condenser lead 2t! through an opening in the sideof the metal shell of the tube, as shown. Insulation for said grid lead from the metal shell of the tube isprovided by a ceramic bushing 2i as illustrated. In asimilar fashion, the plate lead 22 .is brought out through an opening on the opposite side of the tube and insulated from the metal shell of the tube by the ceramic bushing 23.

For convenience of understanding the operation of thepresent invention, there is shown in the right hand portion of Fig. 2 certain of the elements of a succeeding tube similar to theone 'To facilitate the following description, the elements of the said succeeding tube-are designated by the reference characters used hereinbefore with the addition of the letter (1.

Referring again to-Fig. 2, and considering two amplifiers connected as illustrated in said figure, it will be seen that plate 12 is directly connected tothe ceramic coupling condenser l9a by means of the plate and grid leads 22 and 25a. Said leads are rather heavy, so that the series inductance between tubes is minimized. The grid side of said coupling condenser is connected to grid 9d at the top of coil Ilia, which is in series with said grid and its pin in thetube base. In shunt with coil l8a and connected to the lead between the tubes is the plate load resistor i. The position of the circular corrugated diaphragm i l relativeto the upper surface of the anode i2 is varied-by screw I5.

Considering for the moment a comparison of the tuned circuit and coupling in the two illustrations of Figs. 1 and 2, it will be observed that the structure shown in Fig. 2 embodies the output and input capacities 5 and 6 of the stage shown in Fig. 1 as the capacitance shunting coil lta in Fig. 2. The output capacity 5, being the major capacitance, is determinedby the adjustment of diaphragm I i. This adjustmentshouldbesuch as to resonate the coil Ilia inthe following tube at the desired frequency. A tuning capacitance in the neighborhood-of 1 to-3micro-micro farads is usually sufficientior a s0 megacycle I. F.

amplifier.

By means of the present invention, illustrated in the structure of Fig. 2, the lead and socket capacitances l, which were present in the conventional arrangement of Fig. 1, have been eliminated. As a result of this'substantial reduction of shunt capacitance, the inductance of'the coil 3 (Fig. 1) may be substantially increased, thus providing a higher-L/C ratio and correspondingly increased gain.

Attention is now directed to Fig. 3, which illustrates the mounting of a plurality of the tubes on the chassis of a receiver. The metallic shells of the tubes may be grounded by connection to the chassis in any suitable manner. It is particularly interesting to note that the present invention, comprising an amplifier tube with selfcontained .tuned circuit and coupling condenser, permits a much simpler mounting of said tube, and results in a considerable economy of space. For instance, the metal shell of the tube provides the desired shielding of the coil which has been placed within the tube as illustrated in Fig. 2, and in addition, the projection of the plate and grid leads from opposite sides of the tube permits a direct electrical connection of the tubes as shown in Fig. 3. The elements of Fig. 1 which have not been specifically mentioned in the preceding description remain as external circuit components. For simplicity, those elements are omitted in Figs. 2 and 3, especially since the present invention is not concerned therewith. Of the elements hereinbefore specifically mentioned, only the plate resistor 4 is external to the tube, as shown in Figs. 2 and 3, and that element is not bothersome.

While a single preferred embodiment of the invention has been illustrated by the purpose of the disclosure, it will be understood that other forms or embodiments may be employed and that the invention is capable of various modifications.

I claim:

1. A high frequency amplifier tube, comprising an enclosure, electrodes therein including input and output electrodes, an inductance coil .withinsaid enclosure connected to the input electrode and adapted to serve as an interstage coupling element, and means associated with the output electrode for forming therewith an adjustable capacitance.

2. A high frequency amplifier tube, comprising an enclosure, electrodes therein including input and output electrodes, an inductance coil within said enclosure connected to the input elec- 45 trode and adapted to serve as an interstage coupling element, a coupling condenser within'said enclosure connected to the junction between said input electrode and said coil, and means associated with the output electrode for forming therewith an adjustable capacitance.

3. A high frequency amplifier tube, comprising an envelope including .a metallic shell, electrodes therein including input and output electrodes, an inductance coil within said envelope connected to the input electrode and adapted to serve as an interstage coupling element, a flexible metallic diaphragm secured to said shell in such relation to said output electrode as to form therewith an adjustable capacitance, and means extending externally of said envelope for adjusting said diaphragm to varysaid capacitance.

4. A high frequency amplifier tube, comprising an enclosure including a base and'a cylindrical metallicshell, electrodes therein including a control'grid and an anode, an inductance'coil within said enclosure 'havin'g'one end connected to said grid, a contact prong on said base connected to the other end of said coil, input and output leads for said grid and .anode, respectively, extending through the wall of said shell at opposed points and insulated from said wall, and means associated with said anode for forming therewith an adjustable capacitance.

5. A high frequency amplifier tube, compris- 75 ing an enclosureincluding a base and a cylindrical metallic shell, electrodes therein including a control grid and an anode, an inductance coil Within said enclosure having one end connected to said grid, a contact prong on said base connected to the other end of said coil, input and output leads for said grid and anode, respectively, extending through the wall of said shell at opposed points and insulated from said wall, a coupling condenser within said enclosure included in said input lead, and means associated with said anode for forming therewith an adjustable capacitance.

6. A high frequency amplifier tube, comprising an envelope including a base and a cylindrical metallic shell, electrodes therein including a control grid and an anode, an inductance coil Within said envelope having one end connected to said grid, a contact prong on said base connected to the other end of said coil, input and output leads for said grid and anode, respectively, extending through the wall of said shell at opposed points and insulated from said wall, a flexible metallic diaphragm secured to said shell in such relation to said anode as to form therewith an adjustable capacitance, and means extending externally of said envelope for adjusting said diaphragm to vary said capacitance.

7. A high frequency amplifier tube, comprising an envelope including a base and a cylindrical metallic shell, electrodes therein including a control grid and an anode surrounding said grid and having a top surface, an inductance coil within said envelope having one end connected to said grid, a contact prong on said base connected to the other end of said coil, input and output leads for said grid and anode, respectively, extending through the wall of said shell at opposed points and insulated from said wall, a flexible metallic diaphragm secured to said shell above said anode so as to form with the top surface of the anode an adjustable capacitance, and means extending externally of said envelope for adjusting said diaphragm to vary said capacitance.

8. A high frequency amplifier tube, comprising an envelope including a base and a cylindrical metallic shell, an electrode assembly within said envelope including a control grid and an anode, said anode being of cylindrical form and surrounding the other electrodes and having a top surface, an inductance coil within said envelope below the electrode assembly and having one end connected to said grid, a contact prong on said base connected to the other end of said coil, input and output leads for said grid and anode, respectively, extending through the wall of said shell at opposed points and insulated therefrom, a corrugated metallic diaphragm secured to said shell in spaced relation to the top surface of said anode and forming with said surface a capacitance, and means extending externally oi the 6 tube for adjusting said diaphragm to vary said capacitance.

9. A high frequency amplifier tube, comprising an envelope including a base and a cylindrical metallic shell, an electrode assembly within said envelope including a control grid and an anode, said anode being of cylindrical form and surrounding the other electrodes and having a top surface, an inductance coil within said envelope below the electrode assembly and having one end connected to said grid, a contact prong on said base connected to the other end of said coil, input and output leads for said grid and anode, respectively, extending through the wall of said shell at opposed points and insulated therefrom, a coupling condenser within said envelope included in said input lead, a corrugated metallic diaphragm secured to said shell in spaced relation to the top surface of said anode and forming with said surface a capacitance, and means extending ex ernally of the tube for adjusting said diaphragm to vary said capacitance.

10. In a high frequency amplifier tube for use in a cascade arrangement, inductance and capacitance elements within said tube adapted to serve as coupling means between said tube and a preceding tube, and an adjustable condenser within said tube adapted to resonate with the inductance element of a succeeding tube.

11. A high frequency amplifier tube adapted for use in a multi-stage cascade amplifier circuit, comprising an enclosure, electrodes therein including input and output electrodes, input and output circuit connections, an inductance coil within said enclosure connected so as to be in shunt relation with the input circuit, and means associated with said output electrode for forming therewith an adjustable condenser in shunt relation with the output circuit, said inductance coil and said condenser serving as elements of tuned coupling circuits when the tube is employed as one of a plurality of similar amplifier stages in a cascade arrangement.

CHARLES E. DOLBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,735,152 301 Nov. 12, 1929 1,801,022 Poncel Apr. 14, 1931 1,930,499 Zworykin Oct. 17, 1933 1,997,019 Schloemilch Apr. 19, 1933 2,239,303 Purlington Apr. 22, 1941 2,394,397 Mouromtsefi Feb. 5, 1946 1,958,591 Roberts May 15, 1934 2,025,075 Samuel Dec. 24, 1935 2,122,776 Matthies July 5, 1938 2,167,201 Dallenbach July 25, 1939 

